1. Field of the Invention
This invention relates generally to the field of medical prosthetics, and more particularly to a new and improved replacement ligament.
2. Background Information
Replacement ligaments can restore mobility when native ligaments have ruptured beyond repair. However, success of the replacement depends upon proper attachment of the replacement ligament to the host bone and the degree to which the replacement ligament can withstand abrasion during use.
Current designs for emplacement of synthetic ligaments require routing of the ligament through one or two tunnels drilled through bone depending upon whether the over-the-top, modified over-the-top or double tunnel design is employed. In the case of an injured knee joint, the anterior cruciate ligament is replaced by attaching a replacement ligament through tunnels drilled through the femur and tibia from the natural ligament attachment site to an outer surface of the host bone. After passage through the tunnels, the ends of the artificial ligament are usually anchored to the outside of the bones using staples, screws or the like.
The major drawback of such designs is that the ligament moves inside the drilled tunnels during flexion and extension of the knee. If the ligament becomes worn by contact with bone spicules that may form at the entrance to the tunnels, it loses strength and produces particles of ligament debris that cause irritation.
In addition to these drawbacks, the tunnels provide access to the interior of the host bones. As a result, synovial fluid can migrate from the intra-articular region between the host bones into the bone tunnels. Thus, any infection in the intra-articular region can be easily communicated into the interior of the host bones and thereby result in serious intra-osseous complications. Similarly any unhealthy condition within the bones can be communicated to the intra-articular region.
The synthetic ligaments employed in known designs for replacing damaged natural ligaments must meet a wide range of performance requirements, including biocompatibility, high fatigue life, and mechanical properties appropriate to stabilize the involved joint. They are usually constructed of synthetic fibers woven into a cylindrical tube or cord designed to mimic the flexibility and strength characteristics of the natural ligament and to provide sufficient porosity to promote ingrowth of tissue and bone.
Moreover, synthetic ligaments so attached are usually provided with three distinct regions of varying weave structure and porosity designed to meet the requirements of their functions in the three biological regions with which they are in contact. For example, the portion of the ligament which lies between the articular ends of the bones must have high tensile strength and a high degree of abrasion resistance since the intra-articular region includes the portions of the ligament which contact the entrances to the bone tunnels. The portion of the ligament that lies within the tunnels in the bone requires ability to conform to the shape of the tunnel, a minimal elongation under load, and a substantial degree of porosity to enhance ingrowth of bone for permanent fixation of the device to the bone. And the end regions of the synthetic ligament must provide a site having stiffness (minimal elongation under stress) for attachment of the ligament to the bones or for anchorage by tissue and bone ingrowth.
Consequently, it is desirable to have a new and improved replacement ligament and a method for attaching replacement ligaments that overcomes these concerns.